Radio circuits



April 20, 1937. H. F. DALPAYRAT RADIO CIRCUITS Filed Nov. 7, 1934 4 l 97 as INVENTOR HENR! FRANCOIS DALPAYRAT BY We;

ATTORNEY Patented Apr. 20, 1937 UNITED STATES PATENT OFFICE RADIO CIRCUITS Application November '7, 1934, Serial No. 151,813

19 Claims.

My invention relates to improvements in and methods of operating radio circuits, more particularly to regenerative radio receivers, and has for its main object to provide a novel method for obtaining highly stabilized regeneration capable of high signal amplification without producing distortion of the signal amplitudes, and a novel system therefor.

Regenerative circuits as known in the art using a discharge device, such as an electronic relay, usually comprise a feed-back arrangement whereby a portion of the amplified output energy is fed back into the input circuit for reamplification, resulting in greater selectivity and an increase of output signal amplitude.

A disadvantage of regenerative circuits of the type known in the prior art is the fact that their operation is highly unstable and in addition, the stability conditions are different for different receiving frequencies. This makes it practically impossible to operate a radio receiver, using regeneration, reliably and efiiciently over a broad range of receiving frequencies and maintain stable operating conditions, as is well known in the art.

Accordingly it is an object of my invention to provide a new regenerative receiving circuit which is easily stabilized for any desired degree of regeneration and over an extended range of receiving frequencies.

Another disadvantage of regenerative receiving circuits of the type heretofore known in the art is the fact that adjustment of the degree of regeneration is extremely difiicult to carry out, without causing undue distortion or generation of oscillations, producing disturbing squealing noises and similar undesired interference.

Accordingly it is another object of my invention to provide a novel regenerative receiving system in which the degree of regeneration may be accurately and finely regulated close to the point where oscillations set in in such a manner as to make it possible to utilize the advantages of regeneration to the fullest extent Without the danger of producing disturbing oscillations and undesirable distortion.

A further disadvantage experienced with regenerative circuits of known type in the art is the fact that considerable distortion of the signalling amplitude is produced due to the unfavorable shape of the frequency response or resonance characteristic of circuits of this type with regard to a band of signalling frequencies 55 especially in the case of modulated carrier transmission such as in broadcast or similar transmission systems. While producing a very high resonance response, the usual characteristic or resonance curve of regenerative circuits rapidly falls off if the frequency slightly increases or de- 5 creases beyond the resonance frequency, resulting in an undesirable cut-off of the higher modulation side frequencies when receiving broadcast signals or the like comprising a definite band of signalling frequencies (carrier plus side frequen- 10 cies).

Accordingly, a further object of the invention consists in the provision of means in connection with a regenerative or any other type of highly selective receiving circuit by which the unfavor- 15 able relative decreased response of side frequencies differing from the resonance frequency is compensated and a substantially more or less equal or flat top response over a predetermined receiving frequency band is obtained. 20

One of the most highly felt inconveniences in radio reception is the fact that the present day receivers pick up an appreciable amount of noise or disturbing frequencies superimposed upon the power line circuits from which the receivers are operated or directly absorbed by the antenna from neighboring disturbing electric or magnetic fields. These noise currents constitute rather complex current variations containing extremely high harmonic frequencies especially in the case of the most undesirable hissing and crackling noises. As is well known, the noise pick-up of the latter type may be substantially reduced by a sharp tuning of the receiver or any other suitable means for cutting-off extreme side frequencies, such as by adjusting a tone control device now featured in most present day receivers to suppress the higher modulation frequencies, as is well known. In this connection, a system according 40 to the invention can be used in a most simple and efficient manner for eliminating a substantial amount of noise, especially noise of the hissing and crackling character referred to above, by the use of a sharply or highly selective tuned receiving or input circuit such as a regenerative circuit as described by the invention with substantial side band cut-off resulting in a corresponding suppression of noise frequencies, in combination with a novel compensating arrangement according to the invention for restoring the signalling frequencies to their original relative amplitude consistent with good quality reception, thus eliminating distortion of the signals in the output circuit and the connected translating device such as a loud speaker or the like. In this manner, the signal to noise ratio of the receiver may be substantially increased in addition to the increased selectivity, resulting in a substantially higher sensitivity to weak incoming signals.

Accordingly it is a further object of the invention to provide a radio receiving system capable of eliminating a substantial amount of noise and other disturbing frequencies received in such a manner as to secure a high signal to noise ratio with highest possible efficiency of the system and utilization of the incoming signal energy absorbed by the antenna circuit to the fullest degree possible.

Still a further object of my invention is the provision of an eflicient and simple circuit arrangement for adjusting the quality of broadcast receiving signals as desired to suit the personal taste of the listener (tone control).

The invention has further objects and aspects in view which will appear hereafter in the detailed description thereof taken in connection with the accompanying drawing in which I have shown by way of example a circuit arrangement embodying the novel features of the invention.

In the drawing, Figure 1 illustrates schematically a basic regenerative circuit according to the invention in its most simple form with unnecessary elements being omitted for the sake of simplicity, and Figure 2 shows a complete receiving system embodying the new circuit of the invention.

With the above mentioned objects in view, the invention principally involves the provision of at least two feed-back circuits from the output circuit of an electronic relay or similar device to react on the discharge current controlled by the incoming oscillation and interlinking the input and output circuits. The latter result, in accordance with the invention, is obtained by means of at least two grids or similar control electrodes placed in the electron stream, one for receiving the feed-back potential supplied by one feedback circuit and the other for receiving the feedback potential supplied by the other feed-back circuit. The arrangement may be such that the feed-back potentials thus applied to separate grids are normally out of phase and that means are provided for varying the relative phase of the feed-back potentials independently of and without any substantial mutual reaction, other than their combined effect on the common output current of the tube and accordingly the degree of the resultant feed-back on the common electron stream. By this kind of differential feedback action, a very accurate and fine adjustment of the degree of regeneration is obtained within an extremely large range and close to the point where the circuit starts to oscillate in such a manner that highly stabilized regeneration is insured within a desired operating range.

Referring to Figure 1 of the drawing, this shows the basic circuit arrangement embodying the m vention. I have shown an input circuit comprising an inductance I and a variable condenser 2 to which incoming signals, such as broadcast signals, may be applied in any well known manner as shown at z. The circuit l, 2 is coupled to the first grid 5 of an electron tube 3 of known design through a coupling condenser 8. The electron tube is further provided with a cathode 4, a second grid 6, screen grid M and a plate I in accordance with well known design. In this manner, as is well known, signalling potential variations are applied to the grid 5 and amplified current variations are set up in the output circuit of the tube connected between its plate and cathode and indicated at o in the drawing.

Thus far the circuit is similar to any well known amplifier. In accordance with my invention, I provide two feed-back or regeneration circuits from the output of the tube to react upon the electron stream, one feed-back circuit serving to regenerate upon a second separate grid electrode shown at 6. The first feed-back circuit in the example shown is comprised of a condenser H in series with a variable resistance 12, both connected between the plate I and the input side of the coupling condenser 8 in the grid circuit. The second feed-back circuit connected between plate and cathode of the tube is comprised of a resistance 9 in series with capacity l0 and an impedance such as an ohmic resistance l3. In other words, the invention provides at least two high frequency paths shunted across the anode and cathode of the tube 4, one comprising condenser H, resistance l2 and inductance l and the other comprising the resistance 9, the condenser l0 and resistance 13. Suitable tap points from each of these shunt circuits are connected to the grids 5 and 6, respectively, in such a manner that high frequency energy from the output is fed back to both grids 5 and 6 in a desired relative phase and amplitude relation. By varying the resistance 12 or alternatively by varying the resistance 9 or any other element adapted to control the frequency characteristic of the feedback circuits, it is possible to adjust any amplitude and phase relationship between the feedback currents supplied to the two grid electrodes 5 in such a manner as to enable a very fine and accurate adjustment of the entire feed-back system resulting in a substantial stabilization of the operation over a very wide range as has been proven by a series of practical experiments carried out by the inventor. In the example shown, the grid 5 of the tube serves simultaneously as an input grid for applying the incoming oscillations and as one of the feed-back grids in accordance with the invention. As is understood, various other arrangements are possible such as the provision of separate input and reaction grids in place of a single grid 5 as shown.

By the feeding back of independent portions of the amplified output energy to react upon separate parts of the electron discharge stream substantially without any mutual reaction other than the combined effect upon the output current in the anode circuit of the tube, it is readily seen that both feed-back potentials may be easily adjusted independently of each other, thus insuring stability of the system over an extended range of operating frequencies. In order to prevent capacitative reaction through the internal capacity between the grids 5 and 6, I have found it advantageous to provide a screen grid M between the two feed-back grids having a high potential applied to it such as by the connection to the high potential source through a drop resistance I 4 as shown. In this manner it is seen that the two regenerating circuits are extremely loosely coupled through the electron stream passing the two grids 5 and 5 in succession. This accounts for the high relative selectivity of the circuits, while the pure electronic coupling prevents mutual reaction other than with regard to the current flow in the output circuit.

According to a further feature of the invention, it is preferable but not essential to use a tube construction with control grids of substantially equal characteristics for applying the multiple feed-back potentials to the electron stream. The known pentode type tube has been found to be suited for this purpose by using the grid next to the anode (suppressor grid) as the second feedback grid, while the screen serves to prevent capacitative reaction between the feed-back circuits. This has been shown in the practical circuit illustrated by Figure 2.

As pointed out, a circuit of this type, although being highly stable in operation as compared to regenerative systems known in the prior art, has still the disadvantage that the resonance or frequency response characteristic obtained substantially deviates from the ideal shape, resulting in a cut-ofi of the higher side frequencies of a modulated signalling wave received by the system and consequent distortion of the received signal.

The above disadvantage is overcome in accordance with a further feature of my invention by providing a kind of selective regeneration by the design of the regenerative circuits in such a manner that predetermined frequencies or ranges of frequencies are passed more easily by one than by the other, resulting in a different degree of regeneration of these frequencies or ranges of frequencies, respectively. Thus for instance, in the example shown by making the resistance I2 in the one feed-back circuit high and the condenser I! small and by making the resistance 9 in the other feed-back circuit comparatively small and its condenser ill comparatively large, the first circuit becomes more effective in feeding back the higher frequencies while the latter circuit will become more effective in regenerating the lower frequencies such as the high and low notes, respectively, of a modulated carrier signal. In this manner the suppression of the higher side frequencies or higher notes of a receiving signal due to the unfavorable shape of the resonance characteristic of the regenerative circuit or any other preceding highly selective or low noise circuit can be compensated in a simple and most efiicient manner. As tests have shown, it is possible with a system of this type to receive modulated signal energy such as broadcast signals over an extended range of signalling frequencies while maintaining the circuit just below the point of oscillation without any appreciable distortion of the signals as experienced with regenerative receivers of the type heretofore known in the art.

In accordance with a further feature of the invention, the above arrangement may be further utilized for the purpose of reducing disturbing and interfering noises, especially those of a more complex character such as hissing and crackling noises, by purposely distorting the incoming signal to a high degree or substantially reducing the side bands by the use of a highly selective input circuit such as a regenerative system according to the invention, or in other words, by using an input with high signal to noise ratio characteristics. The suppressed side band frequencies are then restored to their original relative amplitude by means of selective regenerative regeneration or compensation system as described by my invention.

A further advantage of a circuit as described is the fact that it may most efficiently and in a very simple manner be used as a tone control device in that by varying the variable resistance I2 or the resistance 9 or by varying any other circuit element in any of the feed-back circuits the relative amplitude of the higher and lower side frequencies may be adjusted at will, resulting in a variation of the tonal quality of the signals received to suit the personal taste of the broadcast listener.

Referring to Figure 2, this shows a complete receiving system embodying the novel circuit according to the invention. I have shown at 15 an antenna connected to ground 94 in series with condenser i6, and a coupling inductance coil l! and a switch 9?. The switch 91 also serves for connecting the receiver to the power supply source which may be either an alternating current or direct current source (universal receiver) according to the example shown. Numeral I9 represents a first amplifying tube of the pentode type having a cathode 36, control grid 3i, screen grid 32, suppressor grid and plate 34. The antenna in the example shown is aperiodic so that signals are received with equal amplitude over a very wide range of incoming frequencies. However, it

is understood that if desired the antenna circuit a and the high frequency input stage may be of the tuned type for increasing the signal to noise ratio of the receiver, as pointed out above. The input signals are applied from the ends of the choke H to the control grid 3i and cathode 36 of the input tube l9. Numeral 33 represents a grid biasing resistance in the cathode lead shunted in the usual manner by a capacity 31. The screen grid 32 is connected through a drop or bleeder resistance ii to the positive pole of the potential supply source to be described later, and is shunted to ground by a by-pass condenser 46 in accordance with well known practice in the art. The ampiified signals in the output circuit of the tube 89 are applied through a coupling condenser 25, vol ume control resistance 2'3 and a grid condenser to the control or first grid 48 of a regenerative vacuum tube serving as both amplifier and detector and frequency compensator as described in connection with Figure l. The anode current for the tube I?) is supplied from the positive pole of a high potential source through a choke coil 25 in the well known manner as shown.

The tube 26 which is also of the pentode type well suited for the purpose of the invention, comprising a cathode 41, screen grid d3, suppressor grid 50 and plate 5|, is connected in a similar regenerative arrangement as heretofore described in connection with Figure 1. One of the regenerative circuits is formed by the con-- denser 52 in series with the variable resistance 53 corresponding to the items H and iii in Figure 1. The other regenerative circuit is formed by the resistance 54, condenser and extension of the input tuning coil 42 corresponding to items 59, it] and I3 according to Figure l. The tuning coil 42 is shunted by a variable condenser 45 for the tuning of. the signal applied to the first or control grid 68 of tube 25 in a manner similar as shown in Figure 1.

Item iii represents a grid leak resistance arranged in a well known manner. The screen grid 48 is connected to the positive pole of the current supply source through the drop resistance t2 shunted to ground by by-passing condenser 5i While the suppressor grid which in this case serves as the second feed-back grid is connected to the junction point between the condenser t5 and the extension tilt of the input tuning coil $2. In the example shown, the latter is provided with a further extension E2 at its other end. The extensions 42 and 42 are connected across a small fixed condenser 43 whereby the circuit formed by the coil 42, its extensions 42" and t2 and the condenserv 43 iii) forms an absorption circuit resulting in a band spread effect with equal response over a predetermined signalling frequency range and furthermore in a band pass filter effect of the system in addition to the regenerative arrangement as described. While the function and the operation of the absorbing circuit has not been fully explained, its effect in further increasing the equal or fiat top response for signals within an extended range of frequencies such as the range covering the broadcast frequencies, is obvious from the observations made, and I do not intend to commit myself to any definite theoretical explanations given in this regard. The circuit connected with tube 20 may be adjusted for operation in a manner similar as explained in connection with Figure 1 so as to obtain high selectivity and efficient amplification in the output circuit of the tube substantially free from distortion.

Item represents a choke coil to prevent high frequency currents from entering the low or andio frequency amplifying circuits. The audio frequency signals obtained in the output circuit of the tube 20 may be amplified in any well known manner by means of an audio frequency amplifier which in the example shown is comprised of two stages, the first stage comprising an amplifying tube 2| having cathode 6?, control grid 68, and a plate electrode 69. The coupling for applying the audio signals is a combined resistance-impedance coupling of known design comprising a coupling resistance 63 and coupling impedance 64 in parallel, coupling condenser 65 and grid leak resistance 66. Item H represents a grid biasing resistance in the oath-- ode lead of the tube shunted by condenser H in a well known manner. The output of the tube 2! is applied through an audio transformer to an output stage comprised of the tube 22 having cathode I4, control grid 15, screen grid 16 and plate '11.. Then 13 is a grid leak resistance connected between the grid 15 and ground. The tube is biased by means of a biasing resistor in the cathode lead shunted by a condenser 8| in a well known manner. The output currents of the tube are applied through a transformer 92 to the operating winding 93 of a translating device such as a loud speaker and the like. The screen grid 76 and the plate 1'! are connected to the positive pole of the current source as shown, while item 1'8 represents a high frequency shunt condenser placed between plate and cathode of the tube in a manner and for the purpose well known in the art.

The current source has been shown to comprise a one-way rectifier 23 having cathode and anode 86 connected in series in the positive lead from the power source and a filter compris ing choke 81 and parallel condensers 88 and 89 with potentiometer resistance 99 shunted to ground by capacity 9|. The receiver may thus be operated from either direct or alternating current in a well known manner in that in the case of direct current supply the rectifier acts as a series impedance while in the case of alternating current it serves for rectification for producing a direct output potental required for the operation of the receiver. The heating circuits of the filaments may be connected in series as is standard with universal receivers of the type shown, such as shown at 38, 41, 67, 'M' and 85' representing the cathode heater windings connected in series with a voltage drop resistance across the current source.

While I have illustrated and described my invention with specific reference to the embodiment according to the drawing, it is obvious from the above that various modifications and variations may be made from the circuit as shown coming within the broader spirit and scope of the invention as pointed out in the ensuing claims.

I claim:

1. An electrical circuit comprising a discharge device having main electrodes and a. plurality of control electrodes, input and output circuits connected to said device, a first feed-back circuit from the output of said device to one of said control electrodes, a second independent feed back circuit from the output of said device to another of said control electrodes, and screening means for reducing electrostatic reaction between said control electrodes.

2. An electrical circuit comprising a discharge device having main electrodes and a plurality of control electrodes, input and output circuits connected to said device, a first circuit means for feeding back amplified output energy to react upon one of said control electrodes, a second independent circuit means for feeding back a1nplified output energy to react upon another of said control electrodes, and means connected in said circuit means for adjusting the relative phase and amplitude relation of the feed-back poten- T tials applied to said control electrodes.

3. An electrical circuit comprising a discharge device having main electrodes and a first grid electrode, a second grid electrode, input and output circuits connected to said device, a first circuit means for feeding back amplified output energy from said output circuit to react upon said first grid electrode, a second independent circuit means for feeding back amplified output energy to react upon said second grid electrode, means for preventing interaction between said first and second grid electrodes, and frequency responsive means inserted in said feed-back circuits for independently regenerating separate ranges of a predetermined signalling frequency band being translated by said circuit.

4. An electrical circuit comprising a discharge device having main electrodes and a plurality of grid electrodes, input and output circuits connected to said device, a first circuit means for feeding back amplified output energy from said output circuit to react upon one of said grid electrodes, a second independent circuit means for feeding back amplified output energy to react upon another of said grid electrodes, frequency responsive means inserted in said feed-back circuits for independently regenerating separate ranges of a predetermined signalling frequency band being translated by said circuit, and a screen grid arranged between said first grids to reduce electrostatic reaction between said first and second feed-back circuits.

5. An electrical circuit comprising a discharge device having input and output circuits and a plurality of feed-back circuits, means for separately and independently applying regenerative potentials to react on different portions of the discharge stream through said device, and means for adjusting the phase and amplitude of the regenerative currents in said feed-back circuits.

6. An electrical circuit comprising a discharge device having input and output circuits and a. plurality of feed-back circuit means for separately and independently applying regenerating potentials to react upon different portions of the discharge stream through said device substantially independently of each other, said feedback circuits being variably responsive to separate frequency ranges of a signal frequency band to be translated by said circuit.

'7. An electrical circuit comprising a discharge device having main electrodes and a plurality of control electrodes, input and output circuits connected to said device, a first feed-back circuit for applying regenerative potential from said output circuit to react upon a first control electrode, a second feed-back circuit for applying regenerative potential from said output circuit to react upon a second control electrode, means for preventing interaction between said first and second control electrodes, frequency responsive means inserted in said first feed-back circuits for regenerating the lower portion of a signalling frequency band, and frequency responsive means inserted in said second feed-back circuit for regenerating the higher portion of a signalling frequency band to be translated by said circuit.

8. The method of operating electric discharge devices which consists in separately feeding back portions of the amplified output signalling energy to react upon separate portions of the common electron discharge stream substantially independently of each other, except in their combined effect on the output signals.

9. The method of operating electric discharge devices consisting in separately feeding back currents of diiferent frequency ranges of a signalling frequency band of the amplified output currents to react upon different portions of a common electron discharge stream separately and substantially independently of each other.

10. An electrical circuit comprising a discharge device having main electrodes and a plurality of control electrodes, input and output circuits connected to said device, a first feed-back circuit between said output circuit and a first control electrode, a second feed-back circuit between said output circuit and a second control electrode, means for preventing reaction between said first and second control electrodes, variable reactance means inserted in at least one of said feed-back circuits for adjusting the frequency responsive characteristic thereof for controlling the feedback frequency range within a predetermined signal frequency band to be translated by said circuit.

11. An electrical circuit comprising a discharge amplifying tube having a cathode, anode and a plurality of control electrodes, signal input and output circuits connected to said tube, a first feed-back circuit for applying a portion of the amplified output signalling energy to one of said control electrodes, a further feed-back circuit for applying another portion of amplified output signal energy to another control electrode, control means for adjusting the phase and amplitude of the feed-back currents inserted in at least one of said feed-back circuits, and a screening electrode having a high positive potential applied to it arranged between said control electrodes to prevent electrostatic reaction between said feedback circuits.

12. I'he method of varying the relative frequency response of an electrical circuit with respect to separate frequency ranges of a given signal frequency band which consists in regeneratively and variably feeding back portions of amplified output energy of different frequency ranges to react upon the input energy substan tially independently of each other.

13. The method of operating regenerative radio circuits consisting in regenerating separate energy portions of the amplified output signal currents to react upon the input signal currents'substantially independently of each other and controlling the relative phase and amplitude relation of the feed-back currents.

14. An electrical circuit comprising adischarge device having a cathode, anode and at least two grid electrodes, input and output circuits connected to said device, a first feed-back circuit for applying regenerative potenial from said output circuit to react upon one of said grid electrodes, a second feed-back circuit for applying regenerative potential from said output circuit to react upon the other of said grid electrodes, frequency responsive means inserted in said first feed-back circuit for regenerating the lower range of a signalling frequency band, further frequency responsive means inserted in said second feed-back circuit for regenerating the higher range of said signalling frequency band, and screening means for preventing capacitative reaction between said feed-back circuits through the inherent capacity between said grid electrodes.

15. A radio circuit comprising a discharge device having main electrodes with means for setting up a space discharge current therebetween and a pair of control grids, an input circuit connected to one of said grids and an output circuit connected to said main electrodes, means for impressing a radio signal upon said input circuit, a feedback circuit for reacting upon the other of said grids with energy derived from the same signal in said output circuit, and means for suppressing mutual coupling between said grids except as afforded by the space current passing the grids in succession.

16. A radio circuit comprising a discharge device having main electrodes, a pair of control grids and a screen grid arranged between said control grids, an input circuit connected to one of said control grids, and an output circuit connected to said main electrodes, means for impressing a radio signal upon said input circuit, and a feedback circuit for reacting upon the other of said control grids with energy derived from the same signal in said output circuit.

17. In a signalling circuit, a discharge tube comprising main electrodes with means for setting up a space discharge current therebetween and a pair of control electrodes, an input and an output circuit connected to said device, means for impressing a radio signal upon said input circuit, independent circuit means for applying separate feedback potentials of predetermined phase and amplitude relation and derived from the same signal in said output circuit to said control electrodes, and means for suppressing mutual coupling between said control electrodes except as afforded by the space current passing the electrodes in succession,

18. In a signalling circuit, a space discharge device comprising main electrodes with means for setting up a space discharge current therebetween and a pair of control grids, an input and an output circuit connected to said device, means for impressing a radio signal upon said input circuit, and individual circuit means for applying separate feedback potentials of predetermined phase and amplitude relation and derived from the same signal in said output circuit to said grids, and means for substantially suppressing mutual coupling between said grids except as afforded by the space current passing the grids in succession.

19. In a signalling circuit, a space discharge device comprising main electrodes and a pair of 5 space current control elements, an input circuit and an output circuit connected to said device,

means for impressing a radio signal upon said input circuit, and independent circuit means for applying separate feedback potentials of predetermined phase and amplitude relation and derived from the same signal in the output circuit to said control elements.

HENRI FRANCOIS DALPAYRAT. 

